Summary Technologies and methods enabling the manipulation and probing of protein function at precise times and locations within complex cells are powerful tools for experimental biologists. The broad aims of this project are to develop a new suite of tools allowing covalent protein linkage triggered by light, which can be used to modulate protein activity, tag proteins, or assemble new protein architectures. In this project, we will combine light-responsive plant-based photoreceptors with genetically-encoded technologies for protein-protein ligation, resulting in new tools in which two proteins can be permanently and covalently linked upon exposure to a flash of light. Our work will explore use of these tools for modulating protein activity for extended periods following a light trigger. We anticipate such tools will have wide utility, enabling spatiotemporal control of protein function, protein tagging, and macromolecular assembly in a completely genetically-encoded module. !